The present invention is directed to a method of operating automatic chemical feeders useful for preparing a liquid solution, e.g., an aqueous solution, of a chemical material, such as a sanitizing chemical, wherein the chemical material is contacted with a fluid in which the chemical material is soluble, i.e., a solvating fluid. The resultant liquid solution is discharged from the feeder and forwarded to the point of application, e.g., a body of water, where it is to be used. In particular, the present invention is directed to method of operating a pressurized chemical feeder so that the feeder automatically dispenses controlled amounts of a solution of a chemical material, e.g., a sanitizing chemical such as calcium hypochlorite, in a reliable, efficient and cost effective manner. Examples of systems that can be treated with aqueous solutions produced by the method of the present invention include water treatment plants, potable water supplies, water for industrial or process usage, waste water systems, water systems for cooling towers, run-off water, swimming pools, hot tubs and the like.
More particularly, the present invention is directed to a novel method of operating pressurized chemical feeders, i.e., feeders that operate under positive pressure, so that only a desired portion of the chemical material charged to the feeder is contacted with solvating fluid. Still more particularly, the novel method comprises establishing and maintaining an atmosphere of substantially inert gas, e.g., air, in the chemical feeder above the soluble chemical material, e.g., a solid chemical material such as calcium hypochlorite tablets, while the feeder is operating, thereby to control the level of solvating fluid within the feeder and hence the amount of chemical material contacted by the solvating fluid. As used herein and as later more definitively defined, the term xe2x80x9csubstantially inert gasxe2x80x9d or xe2x80x9cinert gasxe2x80x9d means a gas that is substantially chemically inert with respect to the soluble chemical material within the feeder.
Chemical feeders for producing solutions of chemical materials are known. Particularly well known are chemical feeders for producing aqueous solutions of chemical materials such as sanitizing agents, e.g., calcium hypochlorite, that are used for the treatment of water and water systems. Typically, such feeders operate by providing a solid composition, which contains a soluble chemical material of a suitable shape, e.g., tablets, pellets or granules, within a suitable chamber and controllably contacting the chemical material (solute) with a solvating fluid, e.g., water or other suitable solvent, thereby to dissolve the chemical material and produce a solution of the chemical material in the solvating fluid or liquid. The solution of chemical material so produced is removed from the feeder and forwarded, directly or indirectly and with or without further treatment (physical or chemical), to the point of application or use. Aqueous solutions of sanitizing agents produced by such feeders have been utilized in various applications, e.g., to disinfect effluent from sewage treatment plants, for sanitizing water used in swimming pools and hot tubs, for the treatment of food supplies and surfaces used in connection with the preparation or treatment of food, e.g., tables, sinks, tanks, walls and floors, and for the treatment of other aqueous streams and water systems. Such feeders have been used also for preparing water-soluble chemicals other than sanitizing agents.
Chlorine, hypochlorous acid and other sanitizing chemicals are used in swimming pool and hot tub applications to control the growth of algae and other organisms in the water. The concentration of the sanitizing chemical in the water, e.g., swimming pool, must be kept between a concentration that is effective to eliminate algae and other objectionable organisms and below a higher concentration that is harmful to the user. Consequently, chemical feeders which produce aqueous solutions of sanitizing agents that are used in the treatment of recreational water for bathing, swimming and hot tubs, have been designed to alleviate the shortcomings that typically accompany periodic manual additions, e.g., by broadcasting of the sanitizing agent over the surface of the recreational water, e.g., a variation in the amount of sanitizing agent added. Examples of chemical feeders are described in U.S. Pat. Nos. 3,595,786; 3,595,395; 4,584,106; 4,732,689; 4,759,907; 4,842,729; 5,089,127; 5,427,748; 5,441,711; 5,447,641; 5,932,093; and 6,077,484.
A feature associated with many chemical feeder installations, such as those described in the above-cited U.S. Pat. Nos. 5,089,127, 5,384,102 and 5,427,748, is that the feeder, when used in a closed system, is installed in close liquid communication with the suction side of a recirculation pump, which results in the feeder operating at or slightly below atmospheric pressure. Such an installation avoids the build-up of pressurized air within the feeder and also the requirements for a feeder design and materials of construction that will withstand positive pressures that are encountered during operation of a feeder at above atmospheric pressures.
Notwithstanding the aforementioned advantages of operating a chemical feeder at atmospheric pressure, there are applications where operating a chemical feeder under positive pressures, i.e., at pressures above atmospheric pressure, e.g., at pressures from just above atmospheric, e.g., 1 pound per square inch gage (psig) (6.9 kPa) to 50 (psig) (345 kPa), is desirable and even required by the particular installation.
Such installations include those where the feeder is located below the level at which the body of water, e.g., the swimming pool, to be treated is situated, e.g., below grade, or where the feeder is in association with a pressurized pipe line, or anytime the pressure at the outlet of the feeder is above ambient pressure. In such installations, the feeder is usually installed in close liquid communication with the outlet side of the recirculation pump, which then must develop at least sufficient force to overcome the static head of pressure represented by the difference in height between the pump and the level of the body of water. For example, water withdrawn from a swimming pool for treatment is forwarded by gravity to a filter and then pumped sequentially to a heater (if used) and the chemical feeder before being returned to the pool. Other arrangements place the filter after the recirculation pump, or position the feeder in a bypass conduit parallel to the main flow line but located on the discharge side of the recirculation pump. A further example is when a feeder is used for the treatment of a potable water supply and the feeder is placed in series with an elevated potable water tank, which is used to supply a water distribution system.
Typically, such pressure feeders are operated in a manner wherein the dissolving or solvating fluid (solvent) introduced into the feeder contacts most or substantially all of the chemical material within the feeder, i.e., the solvating fluid floods the chamber containing the dissolvable chemical material. Such feeders are sometimes referred to as soaker feeders. Further, in the absence of means to allow the solvating fluid to drain out of the soaker feeder when it is not operating, the chemical material in the feeder continues to soak (and dissolve) in the solvating fluid. When xe2x80x9csoakingxe2x80x9d of the chemical material occurs during periods of feeder inoperation, the concentration of the chemical in the solution within the feeder increases above that desired for normal operating levels, results in premature depletion of the chemical material, and the possible occlusion of contiguous openings by partially dissolved and re-crystallized chemical material. In, for example pressure feeders used to sanitize swimming pools, xe2x80x9csoakingxe2x80x9d of the chemical material, e.g., calcium hypochlorite, causes delivery to the pool (when the feeder is subsequently placed in an operating mode) of a solution having a chemical material concentration that is much greater than intended, e.g., the level of chemical material will often be enough to xe2x80x9cshockxe2x80x9d the pool when such a shock treatment is not desired or expected.
When operating a pressurized chemical feeder, it would be desirable to control the level of solvating fluid within the feeder and thereby limit the amount of chemical material within the feeder that is contacted by the solvating fluid. In accordance with the present invention, it has been discovered that by providing a substantially inert gas, e.g., air, within the pressure feeder during its operation, it is possible to control the level of solvating fluid within the feeder, thereby limiting the amount of chemical material contacted by the solvating fluid, which in turn affects the rate at which chemical material in the feeder is dissolved by the solvating fluid and the concentration of chemical material in the solution discharged from the feeder.
In one contemplated and preferred embodiment, substantially inert gas (hereinafter at times referred to as xe2x80x9cinert gasxe2x80x9d) and solvating fluid are introduced simultaneously into the chemical feederxe2x80x94either through the same (a preferred embodiment) or different conduits. For example, they can be introduced into the feeder simultaneously admixed together through the same conduit, as described in connection with FIGS. 1 and 2, or through separate conduits (not shown in the Figures). Alternatively, the solvating fluid can be introduced continuously into the feeder with the inert gas being introduced discontinuously (batch wise) and either separate from or admixed with the solvating fluid. By simultaneous introduction, as used herein, is meant that the solvating fluid and inert gas (when charged to the feeder) are introduced at the same time.
In a second contemplated embodiment, inert gas is introduced into the feeder prior to introducing the solvating fluid into the feeder to establish a first desired pressure within the feeder. Subsequently, solvating fluid is introduced into the feeder, which action will tend to compress the inert gas already charged to the feeder. Additional inert gas can be introduced into or released from the feeder whereby to establish the desired level of fluid in the feeder, to contact the desired quantity of the chemical material within the feeder and establish a second operating pressure within the feeder. Thereafter, solvating fluid and inert gas (as required) are charged to the feeder (through the same or separate conduits) to maintain the operating conditions (pressure, flow rates, solution concentration, etc.) previously established or subsequently desired. In this second embodiment, the additional inert gas can be introduced into the feeder either continuously (simultaneously with the solvating fluid) or batch wise (as make-up inert gas).
In a third contemplated embodiment, solvating fluid is introduced into the feeder to an initial or desired level or height within the feeder, including filling completely the space within the feeder holding the chemical material. Thereafter, inert gas is introduced into the feeder (through the same or a separate conduit) to displace a portion of the solvating fluid (if required) and establish/maintain the desired operating pressure and level of fluid within the feeder, i.e., the fluid-gas interface. Thereafter, solvating fluid is introduced continuously into the feeder; and inert gas (in amounts required to maintain the desired level of solvating fluid, e.g., the height of the gas-fluid interface) is introduced batch wise or continuously into the feeder through the same or a different conduit to maintain the desired operating conditions (pressure, flow rates, solution concentration, etc).
The amount of inert gas introduced into the feeder is sufficient to provide a buffer zone (head space) of inert gas within the feeder. The volume of the buffer zone is selected to limit the amount of chemical material contacted by the solvating fluid, i.e., to limit the level of the solvating fluid within the feeder. The solvating fluid thus is restrained from rising above the gas-solvating fluid interface.
As with any dynamic system, it is understood by those skilled in the art that the operating conditions of the feeder, e.g., pressure, flow rates of solvent and inert gas, chemical material solution concentration produced in the feeder, etc., can change during feeder operation. For example, as the chemical material charged to the feeder is consumed, its volume will need to be replaced by solvating fluid and/or inert gas. Further, some of the inert gas within the feeder will be dissolved or entrained in the solvating fluid passing through the feeder and thereby removed from the feeder during periods that the feeder is in operation. Also, it is possible that inert gas may leak from the feeder through worn seals, etc. This loss/removal of inert gas from the feeder will require that inert gas be introduced into the feeder during operation to replenish gas lost by such circumstances or other operating events. Make-up gas can be charged continuously or intermittently (batch wise) to the feeder. It is understood that inert gas introduced into the feeder in any of the embodiments discussed or contemplated can be introduced either simultaneously with the introduction of solvating fluid and/or intermittently (batch wise) with the introduction of solvating fluid or when solvating fluid is not introduced into the feeder. In either case, the inert gas can be introduced into the feeder admixed with the solvating fluid and/or separate from the solvating fluid. Preferably, the inert gas is introduced simultaneously and admixed with the solvating fluid.
It is understood further by those skilled in the art that the level of solvating fluid within the feeder and hence the amount of chemical material contacted by such fluid can be varied during operation of the feeder by varying the delivery rate of solvating fluid and/or inert gas to the feeder. Some factors determining the desired level of solvating fluid and the concentration of the solution withdrawn from the feeder is the rate of chemical material delivery desired, and the dissolution rate of the chemical material by the solvating fluid, e.g., some solid forms and compositions of chemical material, such as calcium hypochlorite, will dissolve at different rates. For example, the degree of compaction of a solid material composition can effect the rate of dissolution.
In accordance with the present invention, there is described an improved method for dissolving chemical material provided within a container, e.g., a chemical feeder, wherein solvating fluid in which the chemical material is soluble is introduced into the container and into contact with the chemical material provided within the container, thereby to produce a solution of the chemical material, which is withdrawn from the container. The improvement to such method comprises establishing a positive pressure within the container and controllably maintaining an atmosphere of substantially inert gas in the container at least during the period when solvating fluid contacts the chemical material, thereby to control the level of solvating fluid within the container, limit the amount of chemical material contacted by the solvating fluid at any one particular segment of time during periods of feeder operation, and hence control the rate at which the chemical material is dissolved by the solvating fluid and the concentration of chemical material in the solution removed from the container.
The features that characterize the present invention are pointed out with particularity in the claims, which are annexed to and form an integral part of this disclosure. These and other features of the invention, its advantages and the specific objects obtained by its use will be more fully understood from the following detailed description and the accompanying drawings in which preferred embodiments of the invention are illustrated and described. In the drawings, like reference characters designate like parts.
Other than where otherwise indicated, all numbers and values used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d